Kernel panic at Ubuntu: IMA + Apparmor

[Al Viro]

On Sat, Apr 26, 2014 at 07:54:47PM +0300, Dmitry Kasatkin wrote:
> On 26 April 2014 16:56, Al Viro <viro at zeniv.linux.org.uk> wrote:
> > On Sat, Apr 26, 2014 at 11:58:45AM +0300, Dmitry Kasatkin wrote:
> >
> >> Conflict with Apparmor means with Ubuntu.
> >>
> >> But answering to your early question..
> >> IMA does not want permission denied when measuring and re-measuring files.
> >> may_open() is doing that job before.
> >>
> >> We need quickly introduce kernel_read without LSM checks...
> >
> > *snarl*
> >
> > What we need quickly is to introduce you to a textbook or two.  As the
> > matter of fact, in this case even wikipedia might suffice...
> >
> 
> Hopefully we have you who were introduced to a textbook or two about relevant
> subject and able kindly help us with the solution instead of telling
> me this crap...

See the discussion of that very topic (required modifications of vfs_read())
upthread.  And Eric has a very good point about the usefulness of understanding
the basics of IO-related system calls in Unix for anybody who does any
kind of development related to keeping track of file contents modifications,
etc.  It's *not* about some arcane knowledge of VFS internals (which also might
come handy when sticking hooks into said internals); it's about being familiar
with the semantics of read(2) and related concepts.